The present disclosure is directed to a pipeline pig, especially a pipeline pig to be used in cleaning a series of connected pipes where the pipes change in diameter. When change occurs, the engagement between the side wall of the pipe and the pig will change, and if it changes excessively, the pig can stick. This is highly undesirable, namely, it damages the pig, perhaps destroying it, and creates pressure surges in the lines to move the stuck pig. Eventually of course, the stuck pig will be pushed aside, destroyed, or in some fashion overcome by fluid flow.
The present disclosure is directed to a pipeline pig which is constructed to traverse transitions in pipe diameter. Consider an example which will be given of a nominal 8 inch line with a pig sized for that size of line. Therefore, using an 8 inch line as an example, the present disclosure sets forth a pig with a number of disks in the pig which are made oversized slightly. The oversized disks assure proper contact. Yet, because the disks are oversized, they run the risk of jamming. The present disclosure sets forth a disk equipped body where the disks are made of soft material, the material enabling the disks to fold back over the pig. So to speak, as the pig moves from a high pressure insertion point to a low pressure end, the disks are swept behind the pig. This bends or folds the several disks, thereby enabling the disk to swipe the surface. The disks are made of relatively thin construction in the context. Therefore, the disks are able to fold back, and they compress somewhat thereby providing an adequate wiping surface which is expanded during such constricted transmission along the pipeline. More importantly, the present disclosure defines a spacing and disk construction so that two adjacent disks do not fold back on top of each other thereby achieving excessive thickness. To consider the example just mentioned, using an 8 inch pipeline, the disks are made oversized in diameter by of about 5%-10%, and have a disk thickness of about 10% or less, both being calculated on the basis that the nominal ID of the pipeline equals 100%. The pig is constructed with several disks, the preferred number being at least about 3 to maintain the pig in a concentric and aligned posture within the pipeline. The pig is preferably equipped with several such disks t he preferred embodiment being a whole number integer N where N is preferably in the range of about 4 to 12, and more preferably 6 to 8. More than 12 and fewer than 3 define pigs that are inappropriate.
To enable this kind of pig to travel along a pipeline and especially a pipeline made with changes in diameter, the pig is preferably constructed with a set of disks joined to the body. The preferred form of construction is a single piece construction or alternately plural pieces which are adhesively joined together, alternating between large disks and small donuts. Each donut is a circular blank. The disks and the circular donuts (sometimes known as a torus) are constructed of a common material. This common material is an open cell foam of a specified density. The several disks support and space apart the several donuts. The donuts are painted with a surface layer of heavy duty polyurethane which provides greater hardness. The hardness is sufficient that the body of the pig has greater durability. Effectively, when the disks are assembled with the several donuts, a unitary body is formed, again which can either be single piece construction or adhesively joined donuts alternating with the disks.